1. Field of Invention
The present invention relates to a method of driving an electro optical device where gray-scale display is controlled by a sub-field drive method, a drive circuit and an electronic apparatus thereof.
2. Description of Related Art
In the related art, an electro-optical device, such as a liquid crystal display using liquid crystal as electro-optical material, for example, can be unitized for a display portion of various kinds of information apparatus, liquid crystal TV, etc., as a display device that can replace a cathode ray tube (CRT).
Such a liquid crystal display device, for example, includes pixel electrodes arranged in a matrix, an clement substrate including switching elements, such as TFT's (Thin Film Transistors), connected to these pixel electrodes, an opposite substrate including an electrode opposite to each of the pixel electrodes and liquid crystal as electro-optical material filled between these substrates.
A display mode of such a liquid crystal display device includes a normally white mode where a white image is displayed without voltage, and a normally black mode where a black image is displayed without voltage.
Next, an operation of displaying gray scale of an image with a liquid crystal display device is explained.
A switching element is turned on by a scanning signal supplied via a scanning line. An image signal in response to gray scale is applied to a pixel electrode via a data line under the state where the switching element is in an on-state by applying the scanning signal. Then an amount of electric charge in response to voltage of the image signal is accumulated between the pixel electrode and an opposite electrode. This state of electric charge accumulation can be maintained in each electrode by capacity nature of a liquid crystal layer and storage capacitance after accumulating electric charge, even if the switching element is in an off state by removing the scanning signal.
Hence, the orientation state of liquid crystal can be changed every pixel by driving each of the switching elements and controlling the amount of accumulated electric charge in response to gray scale so that transmittance ratio of light is changed and brightness can be changed every pixel. Thus, it is possible to realize a gray-scale display.
In consideration of capacitive nature of the liquid crystal layer and of storage capacitance, it is preferable that electric charge be applied to the liquid crystal layer of each pixel only during a part of a period. Therefore, when plural pixels arranged in a matrix are driven, the scanning signal is applied to pixels connected to each other on the same scanning line simultaneously and the image signal is applied to each pixel via a data line and the scanning line to supply an image signal is switched sequentially. Namely, in the liquid crystal display device, it is possible to attain time-sharing multiplex drive when the scanning line and the data line are shared commonly for plural pixels.
However, the image signal applied to the data line is voltage in response to gray-scale, namely analog signal. Hence, an overall apparatus is highly expensive since an analog circuit or an operational amplifier is necessary for a peripheral circuitry of an electro-optical device. In addition, non-uniformity of display quality occurs due to characteristics of the analog circuit and operational amplifier and/or irregularity of wiring resistance, so that it is difficult to maintain high quality displaying. These problems become especially serious in the case of displaying a fine and accurate image.